I've had this happen on a couple of occasions. These have ONLY been during massive co-operation missions in the MA, say about 10 people or more, with lots of bomber formations on the screen. In other words, where my frame rate drops to low teens or so. I don't recall ever loosing AHV during jabo or fighter missions. Framerates are much better then.
The symptoms are that someone's name gets "stuck" (yellow, "radio 5" channel) in the top right corner and I cant hear anyone. Not even the one whose "name is stuck". I can transmit fine and others can hear me.
When this happens, I'm usually not the only one. A couple of other guys usually loose AHV as well.
Like I said, this has happened only on a couple of occasions under heavy CPU load. Not really a problem for me. Re-starting AH is enough, I've never had to reboot.
I have a SB Live! soundcard. I have to give that "drop acceleration down a notch" a try.
Camo